Currently, various frequency bands are becoming available to sufficiently compensate for deficient frequency bands as mobile communications become common and wireless broadband data communications become activated. The mainly used frequency bands are low frequency bands (698 to 960 MHz) and high frequency bands (1.71 to 2.17 GHz or 2.3 to 2.7 GHz). Further, the multiple antenna based MIMO (Multiple Input Multiple Output) technology is an essential technology for increasing data transmission speed, and is applied to recent mobile communication network systems such as LTE (Long Term Evolution) and Mobile WiMAX.
However, when a plurality of antennas are installed to support the MIMO at various frequency bands, installation costs increase and tower spaces for installing antennas are significantly insufficient in an actual external environment. Further, tower rent costs increase and antenna management efficiency becomes an important problem.
Thus, triple band antennas are urgently requested instead of dual band antennas. While a high frequency band is inserted into an installation space for a low frequency band antenna and thus a width of the low frequency band antenna may be maintained according to a dual band antenna, it is difficult to insert a high frequency band antenna without increasing an antenna width when a triple band antenna is realized.
Meanwhile, due to a fear of common people that electromagnetic waves radiated from an antenna are harmful to human bodies, mobile communication providers conceal antennas if possible and decorate antennas in an environment-friendly way, making sizes of antennas important. Further, since installation of antennas tends to be prohibited unless local residents agree with the installation, recent mobile communication network antennas can be changed and installed only if the widths of the antennas do not exceed a width (for example, about 300 mm) of a conventionally installed low frequency antenna. Of course, classical problems such as a wind pressure load and a load applied to a tower still exist.
Thus, although triple band antennas are urgently requested in recent mobile communication network systems, a conventional wide antenna width cannot be allowed in the market.